Stabilized halogen-containing olefin polymer compositions and stabilizer therefor



United States Patent 3,367,906 STABILIZED HALOGEN-CONTAINING OLE- FINPOLYMER COMPOSITIONS AND STA- BILIZER THEREFOR Richard B. Lund,Whippany, Arleen C. Pierce, Parsippany, and Edith Turi, Livingston,N.J., assignors to Allied Chemical Corporation, New York, N.Y., acorporation of New York No Drawing. Original application Mar. 24, 1964,Ser. No. 354,448. Divided and this appiication Apr. 6, 1967, filer. No.646,781

4 Claims. (Cl. 260-45.7)

ABSTRACT OF THE DISCLOSURE The present invention relates to the thermalstabilization of chlorinated ethylene polymer by the addition of oz,a-diphenoxy-2,3,5,6-tetrachloro-p-xylene or an alkyl derivative thereof.

This is a division of application Ser. No. 354,448, filed Mar. 26, 1964.

It is known that halogen-containing polyolefins such aspolyvinylchloride, chlorinated polyethylene and chlorinatedpolypropylene are adversely affected when exposed to elevatedtemperature either during fabrication or during use. This adverse effectis usually evidenced by a darkening in color, and an increase inviscosity which is demonstrated by the increased Work required toextrude or mix the material. It is generally believed that this changein viscosity is due to splitting hydrogen and/or chlorine atoms out ofthe polymer molecule, resulting in increased crosslinking of thepolymer.

Additives have been proposed in the prior art for increasing the thermalstability of specific halogen-containing polyolefins, however, there isno consistency in the effectiveness of these stabilizers when used indifferent types of halogen-containing polyolefins. For instance, anumber of compounds which effectively stabilize vinyl chloride compoundshave little or no stabilizing effect on chlorinated polyethylene.Another factor to be considered in the selection of a thermal stabilizeris the presence of a metal constituent in many of the prior artadditives. These metal-containing stabilizers, such as metal salts,metal phenolates and organo-metallic compounds, are frequentlyincompatible with the polymer, causing loss of transparency,discoloration and nonhomogeneous appearance.

It is an object of the present invention to provide heat stablecompositions based upon chlorinated polyethylene.

Another object of the present invention is to provide metal-free organicstabilizers for, and compatible with chlorinated polyethylenes.

Additional objects and advantages of the present invention will becomeapparent from the following detailed description thereof.

In accordance with the present invention it has been discovered that thethermal stability of chlorinated ethylene polymer is improved by theaddition thereto of at least one member of the group consisting ofm,oc'-diphenoxy-2,3,5,6-tetrachloro-p-xylene and alkyl derivatives ofa,a'-diphenoxy-2,3,5,fi-tetrachloro-p-xylene. The new class of compoundscan be represented by the formula:

wherein R is a hydrogen or alkyl group of 1-5 carbon atoms. Illustrativeof the stabilizing additives of the present invention are, for instance,a,a-diphenoxy-2,3,5,6-tetrachloro-p-xylene anda,a-bis-(2-niethylphenoxy)-2,3,5,6-tetrachloro-p xylene:

c1 (:1 CH3 wherein R is either hydrogen or an alkyl group of 'l-5 carbonatoms and A is an alkali cation, for instance either sodium phenolate ora derivative thereof substituted in the orthoposition by an alkyl group,with u,ct-2,3,5,6- hexachloro-p-xylene in accordance with the followingequation:

wherein R is an alkyl group of l-S carbon atoms.

The stabilizers can be employed with other common additives used inhalogenated polyolefin formulations, such as stabilizers against theeffects of radiation, fillers, pigments and dyes. The stabilizer can beincorporated into the polymer formulation by any known blendingtechnique.

The effectiveness of these stabilizers can be measured by determinationof the extent of crosslinking which is occasioned in the polymer byexposure to elevated temperatures. This crosslinking can be measured bythe amount of gel formation. The latter can be determined as thepercentage of the polymer, originally entirely soluble inmonochlorobenzene, which is no longer soluble after the heat treatment.Gel formation increases viscosity and slows the rate of extrusion of thepolymer if extrusion is carried out at a constant pressure on thepolymer.

A further measure of effectiveness of stabilization is the comparison ofcolor of the unstabilized material with that of the stabilized materialafter both have been exposed to elevated temperatures.

The chlorinated polyethylene stabilized by our invention can containfrom about 20 to about by weight chlorine. In a preferred embodiment,the chlorinated polyethylene is randomly chlorinated whereby it isessentially amorphous and has a low brittle point (glass transitiontemperature), such as about 0 C. or lower at 20 percent chlorine contentand rising with chlorine content to over-185 C. at 80 percent chlorinecontent. Particularly suitable polyethylenes to be chlorinated for usein our invention are those produced as described in Example 6 of BritishPatent No. 858,674, of Jan. 11, 1961. Such polyethylenes can bechlorinated with advantage for use in our invention by the processdescribed in Example 3 of French Patent No. 1,316,044 of Dec. 17, 1962.

The polymerization process of British Patent No. 858,674 resultsgenerally in a polymer of high molecular weight such as 500,000 to5,000,000 average molecular weight, and of density of about 0.935 to0.96 gin/cm. at 25 C. The molecular weight of the polymer can be reducedby a thermal treatment, for instance in accordance with the processoutline at page 12, lines 7377 of the above-identified British PatentNo. 858,674. The molecular weight of the resulting polyethylenes will bein the range of about 20,000 to 300,000, and the density will be about0.94-0.95 gm./cm. at 25 C.

The foregoing molecular weights are calculated from the intrinsicviscosity of a solution of the polymer in Decalin, according to themethod of P. S. Francis et al. (Journal of Polymer Science, vol. 31, pp.453466), i.e. by using the following formula:

where [7]] is the instrinsic viscosity in deciliters per gram, and M isthe average molecular weight.

When polyethylenes of molecular weights such as 100,000 and below arechlorinated for use in our invention, solution chlorination methods canbe used to advantage to obtain the desired amorphous products.

The glass transition temperatures above cited can be determined by astandard test for stiffness (ASTM test -D-104361T), as the temperaturebelow which the stiffness sharply increases so that the sample becomesbrittle. A typical stiffness modulus at the glass transition temperaturefor the subject chlorinated polyethylenes is 1.45 1O p.s.i. (i.e. 10dynes/cm.

One preferred group of randomly chlorinated polyethylenes of chlorinecontent in the range 2080 percent by weight used in our invention, willhave relatively high intrinsic viscosities from about 1.5 to about 5deciliters per gram, indicating high molecular weight. Other useful andpreferred chlorinated polyethylenes, not necessarily amorphous, willhave intrinsic viscosities from about 0.1 to about 1.5 deciliters pergram, indicating lower molecular weight of the polymer. These intrinsicviscosities are determined upon a 0.1 gram per 100 ml. solution inodichlorobenzene at 100 C.

The following examples describe completely specific embodiments of ourinvention and illustrate the best mode contemplated by us of carryingout our invention; but are not to be interpreted as limiting theinvention to all details of the examples.

The samples tested consisted of unstabilized controls and compositionscontaining stabilizer in an amount equal to 4% by weight of the weightof the chlorinated polyethylene. In all tests the chlorinatedpolyethylene sample was ground to about 40 mesh powder. The stabilizerwas dissolved in a volatile solvent, such as methanol. This solution wasedded to the powdered polymer and the mixture was stirred under N atambient temperatures, until completely dried.

About 2-3 grams of each prepared sample were heated in open test tubesin a block heater at 200 C. for 60 minutes, except where specifiedotherwise. This heat treatment of the sample resulted in the thermalbreakdown of the polymer into a certain percentage of a crosslinkedproduct,-or gel; as well as resulting in a discoloration of the polymer,manifested by darkening. The quantitative value of the discoloration wasmeasured using a reflectance meter with a green filter, by comparing thereflectance of the sample to that of a standard white magnesium oxidesample. The reflectance reading obtained on the discolored sample wasthen expressed as percent white- 4 ness, the reflectance of the standardbeing taken as whiteness.

The amount of crosslinked product or gel formed as a result of the heattreatment was determined in accordance with the following procedure.

About 0.2 to 0.3 gram of the heat treated polymer was weighed into atared stainless steel basket made of 250 mesh screen. This basket wasplaced into a Soxhlet extractor containing approximately ml.monochlorobenzene, and refluxed for six hours. The noncrosslinkedproduct was extracted, permitting gravimetric determination of thecrosslinked gel. During the extraction the system was kept under slow Nstream to prevent oxidation.

Examples 1-3 TABLE I S tabilizcr Percent Percent Whitcncss (5 clUnstabilized rosin control I. 12 3 a x-diphenoxy-2,3,5,0-tetrachloro-"lone" 15 0 a,e -bis(2-metl1ylphenoxy)- 3,5,0 chlorop-xylnne 16 0 InTable II comparative results are shown with the same resin base used forthe tests shown in Table I, the heat treatment here being 230 C. for 30minutes.

TABLE II Stabilizer Percent Percent whiteness Gel Unstabilized rosincontrol 4 16 a,a-bis(2-mcthylphenoxy)-2,3,5,(i-tctracl1loropxylenc (5 5In the following, examples are given showing exemplary processes for thepreparation of each of the novel compounds of the invention.

Example 4 2.3 parts by weight sodium were added to a solution of 9.4parts by weight phenol in 100 parts by volume dry benzene. The resultingmixture was heated with reflux for one hour. The formed solid wasremoved by filtration and dissolved in parts by volumedirnethylformamide with heating. A 16.0 parts by Weight portion of max-2,3,5,6-hexachloro-p-xylene was added to the solution and the reactionmixture heated with reflux with stirring for 47 hours. The reactionmixture was then cooled to room temperature and the resulting solid (3.0parts by weight) was removed by filtration. This solid had a meltingpoint of 198.5-200 C. and was confirmed to be a,e-diphenoxy-2,3,5,6-tetrachloro-p-xylene by elemental analysis and infraredspectroscopy.

Example 5 2.3 parts by weight sodium were added to a solution of 10.6parts by weight o-cresol in 100 parts by volume dry benzene. Theresulting mixture was heated with reflux for one hour. The formed solidwas removed by filtration and dissolved in 150 parts by volumedimethylformamide with heating. A 3.2 parts by weight portion of OC,OL'-2,3,5,6-hexachloro-p-xylene was added to the solution and the reactionmixture was heated with reflux with stirring for 28 hours. The reactionmixture was then cooled to room temperature and the resulting solidremoved by filtration. This solid was recrystallized from dioxane togive 4.6 parts by weight c rd-bis(2-methylphenoxy)2,3,5,S-tetrachloro-p-xylene having a melting point of 237.5-239 C. Thecompound was confirmed by elemental analysis and infrared spectroscopy.

We claim:

1. A composition comprising a chlorinated polyethylene, and astabilizing compound having the formula:

R C1 01 R III 1 I H I l Cl Cl wherein R is a member of the groupconsisting of hydrogen and alkyl of 1-5 carbon atoms.

2. The composition of claim 1, wherein said chlorinated polyethylene isa chlorinated homopolymer of ethylene having a chlorine content of20-80% by weight of said chlorinated polyethylene, having a low glasstransition temperature below 0 C. for a polymer of 20% chlorine contentand rising up to over 185 C. for a polymer of 80% chlorine content, andsaid stabilizing compound is present in a concentration of 0.5 to 10% byweight of said chlorinated polyethylene.

3. The composition of claim 2, wherein said stabilizing compound is ad-bis(Z-methylphenoxy)-2,3,5,6-tetrachloro-p-xylene.

4. The composition of claim 2, wherein said stabilizing compound isa,a'-diphenoxy-2,3,5,6 tetrachloro pxylene.

References Cited UNITED STATES PATENTS 9/1959 Gordon 26045,7 4/1967 Lundet a1. 260-45.7 X

